Euwallacea fornicatus: host range studies in Israel and California (US)
Studies on the host range of Euwallacea fornicatus (Coleoptera: Curculionidae: Scolytinae – EPPO A2 List as part of E. fornicatus sensu lato) have been carried out in Israel and California (US), two areas which are part of the invaded range of this insect originating from Southeast Asia. In Israel, surveys were conducted from 2013 to 2020 in different habitats, including public parks, botanical gardens, private gardens, ornamental landscapes and commercial avocado orchards with surrounding woody vegetation. In California, surveys were carried out in botanical gardens, arboreta, as well as in native and urban forests.
During these studies, 3 tree categories were defined:
- Reproductive hosts: when eggs, larvae, pupae or callow adults of E. fornicatus were detected in galleries and the associated fungus, Fusarium euwallaceae, was detected.
- Non-reproductive host: when typical symptoms of insect attack were observed (usually associated with detection of F. euwallaceae) but without any signs of beetle reproduction.
- Non-attacked trees: when trees were not affected although observed in the vicinity (within a radius of 25 m) of attacked trees.
In total 583 tree species were examined, and host species could be classified as a ‘non-reproductive hosts’ (55.9%) and ‘reproductive hosts’ (13.8%). No particular correlation could be found between host tree phylogeny and susceptibility to E. fornicatus. It is suggested that the beetle reproduction success rate over a wide host range, as well as the long list of species belonging to the ‘non-reproductive host’ category, result from interactions between the beetle fungal symbiont, F. euwallaceae, and sapwood of the attacked tree; the host range suitable for successful reproduction of the beetle being determined by the development of F. euwallaceae.
A list of tree species that are hosts of E. fornicatus can be found in the EPPO Global Database: https://gd.eppo.int/taxon/EUWAWH/hosts
Sources
Mendel Z, Lynch SC, Eskalen A, Protasov A, Maymon M, Freeman S (2021) What determines host range and reproductive performance of an invasive ambrosia beetle Euwallacea fornicatus; lessons from Israel and California. Frontiers in Forests and Global Change 4, 654702. https://doi.org/10.3389/ffgc.2021.654702